Differential condenser circuits



Sept. 16, 1941. H, BERTHOLD DIFFERENTIAL CONDENSER CIRCUITS Filed June7, 1939 fimenfor: Hans Berthold by Patented Sept. 16, 1941 DIFFERENTIALCONDENSER CIRCUITS Hans Berthold, Berlin, Germany, assignor to C. LorenzAktiengesellschaft, Berlin-Tempelhof, Germany, a company ApplicationJune 7, 1939, Serial No. 277,784 In Germany June 16, 1938 2 Claims.

This invention relates to differential condenser circuits, and moreparticularly to circuit arrangemerrts in which one or more tuning orsimilar circuits are coupled to an oscillatory circuit which comprises adifferential condenser adapted to perform amplitude or other regulationof the last mentioned circuit.

It is a well known fact in the art that severe difficulties areencountered in rendering a further circuit or circuits independent ofthe relative position of adjustment of the heretofore known differentialcondensers which for the purpose of effecting adjustment of any kind hasbeen used in an oscillatory or other circuit with which the firstmentioned circuit or circuits are coupled. These difficulties are due tothe fact that the effective capacity of a circuit including adifferential condenser strongly depends upon the position of the rotorplate thereof relative to the stator plates, and that a capacity changeof the circuit in response to a position change of the movable platewith respect to the stationary plates simultaneously affects the othercircuits in an undesired sense.

My invention has for an object to overcome the difliculties mentioned inthe foregoing by so dimensioning a differential condenser forming partof an electric circuit that an angular adjustment of its rotor relativeto the stator plates in order to effect amplitude regulation has noinfluence upon another circuit or circuits being coupled to the firstmentioned electric circuit.

The invention will be more readily understood from the followingdescription taken in conjunction with the accompanying drawing, inwhich:

Fig. 1 shows a known circuit arrangement 6X- planatory of the art, Fig.2 is an equivalent circuit of that shown in Fig. 1, Fig. 3 is adiagrammatic showing according to .the present invention, Fig. 4 showsthe configurations of the various plates or vanes of a diiferentialcondenser designed in accordance with this invention, while Fig. 5schematically shows one embodiment to which my novel differentialcondenser is applied.

A circuit arrangement of conventional design is shown in Fig. 1, inwhich a tuned oscillatory circuit K1 is coupled with a further electriccircuit K2 including a differential condenser D connected to one of thestationary plates 0. and b, respectively, of the differential condenserD. The voltage source or generator G, the capacitive impedance of whichis represented by the reference Cs is applied to the circuit K2 betweenthe tapped mid-point M of the inductance S and the rotor L of thedifferential condenser D. The difficulties mentioned in the foregoingwill be easily appreciated by taking the present conditions underconsideration, since as a matter of fact the effective capacitance atthe terminals A and B of the inductance coil depends upon the relativeposition of the rotor of a differential condenser heretofore employed incircuits of this kind. A change in capacity in response to an an-' gularmovement of the rotor plate relative to the stator plates for thepurpose of amplitude regulation will be transferred to the oscillatorycircuit K1 which will become detuned.

According to the main feature of this invention, the differentialcondenser is so designed and dimensioned, that the effective capacity ateach terminal of the voltage divider or inductance S connected therewithremains constant independent of the angular position of the rotor plateor vane to the stator plates thereof.

The total capacity across the voltage divider or inductance S in Fig. 1will now be more closely considered in conjunction with the equivalentcircuit of Fig. 2 which shows the individual component capacitances intowhich the total capacity may be decomposed. These component capacitancesare partially constant and partially variable in response to an angulardisplacement of the rotor plate relative to the stator plates as willhereinafter be fully explained. In Fig. 2, the reference C2 representsthe constant shunt capacity or initial capacity between the twostationary condenser plates at and b of Fig. l which may be measuredwhen the rotor plate L is removed. The constant capacity of the outercircuit, that is, across the rotor of the differential condenser and thetapped mid-point M between y the terminals A and B of the inductance Sindi- .uration that the sum of the variable capacitances,

i. e. c+cb remains constant.

The capacity between the rotor and the tapping point M is thus constant,but that between the terminals A and B is highly variable particularlyat a low capacity Cs. The maximum value exists in the central positionof the condenser when Cs: and CAB=.250amax., while the minimum value isreached in the end position of the rotor, that is, when Cs=0 and CAB=CQ.

Because of the fact that the impedances and L to o respectively, arealways larger than the impedance across the terminals A and B of theinductance S by hearing in mind the fulfilled condition of resonance,the capacitance across the terminals A and B, hereinafter referred to asCAB may be defined as follows:

Let the voltage from A to B be equal to E. Assuming an ideal coil andcoupling between turns, the voltage drop due to current in the coil willbe negligible and the voltage across the condensers Cs and Ch will beequal to E since the coil is tapped at its mid-point. Accordingly thefollowing mesh equations may be set up:

C'bC', 0,,Cs) z 2 c,,+ C,,+ Cs The capacitive current from A to B is:

Since this last expression shall remain constant in response tovariations of Ca and Cb, it may be rewritten as follows:

In'the last expression, It is a constant, the magnitude of which isdetermined by the component capacitances in either of the outerpositions of the rotor, e. g. when 017:0 and Ca=Cmax., in which case:

k mnx. CS

4 imax.

In this formula, Cmax. represents the maximum values of the componentcapacitances Ca and Cb,

respectively, that is, the nominal capacity of the condenser.

Now, the plates of a differential condenser capable of involving themaximum capacity Cmax. at a constant capacitance Cs of the outer circuitbetween the rotor plate L and the tapping midpoint M of the inductance Sin Fig. 1, without subjecting the inductance S as a whole to anycapacitance changes in response to an angular displacement of the rotorplate relative to the stator plates must, according to one feature ofthis invention, be so dimensioned that the following relationship existsbetween the component capacitances Ca and Cr:

C +(0.25Csk) The ratio of Ca to Cb is diagrammatically shown in Fig. 3in response to a given magnitude of the capacitance Cs. Suchcharacteristic is secured in accordance with still another feature ofthis invention by the use of a semicircular rotor plate R, and statorplates S1 and S2 of falcated configuration as shown in the Fig, l.

The Fig. 5 schematically embodies a radio direction finding receiver inwhich a differential condenser according to this invention is applied inorder to erforrn voltage regulation in the non-directional auxiliaryantenna system thereof. In this embodiment reference letter I-I denotesthe auxiliary antenna and RA the directional frame aerial coupled to theinput tube E of a receiver over an oscillatory circuit Kg whichcorresponds to the circuit K1 of Fig. 1, and

a detuning of which shall be avoided. The differential condenser Ddesigned and dimensioned in accordance with the rule disclosed by thisinvention is adapted to control the voltage of the auxiliary antenna H.Because of the fact that the capacitance between the points or terminalsA and B remains constant independent of the relative position of therotor plate to the stator plates of the differential condenser D, nodetuning of the oscillatory circuit Kg will result from a regulation ofthe voltage of the auxiliary antenna H. In the case under consideration,the capacity of the auxiliary antenna H corresponds to the constant loadcapacity Cs above referred to.

What is claimed is:

1. An electric circuit arrangement comprising a voltage divider coil anda constant capacity circuit across the ends of said coil comprising avariable condenser comprising a semi-circular plate rotatable about anaxis and a pair of stationary plates disposed on opposite sides of saidaxis and parallel with the plane of said rotatable plate and in capacityrelation therewith, the adjacent edges of said stationary plates havinga concave falcate shape, and a substantially fiXed capacity connectedbetween said rotatable plate and the center of said coil.

2. An electric circuit arrangement comprising a voltage divider coil anda constant capacity circuit across the ends of said coil comprising avariable condenser comprising a rotatable plate and a pair of stationaryplates in capacity relation therewith, and a substantially fixedcapacity connected between said rotatable plate and the center of saidcoil, said plates having shapes and relative positions determined by:

